In order to meet the increasingly stringent emissions regulations, diesel engine manufacturers are exploring different avenues for reducing the regulated components of diesel engine emissions. One approach is to increase the injection pressure of the fuel that is injected into the combustion chamber to achieve a more complete mixture of the fuel and air. Although there are a number of different types of fuel injection systems used to achieve the higher injection pressures, the common rail type of fuel system has become increasingly popular. Many of today's common rail fuel systems rely solely on a high-pressure pump to achieve the desired injection pressures. However, as the desired injection pressures increase, it has become increasingly difficult to manufacture high-pressure pumps that are efficient enough and robust enough to consistently and reliably provide fuel at such high pressures, and at the same time, balance cost, weight, packaging, and a multitude of other factors.
One of the primary issues that manufacturers must address is the structural integrity of the portions of the pump that are exposed to the high pressures generated by the pump. At these high pressures, the forces applied by the pressurized fluid can create significant tensile stresses within the material forming the structural portions of the pump. This is especially true at areas where there may be stress concentrations, such as at corners or edges of bores. In addition, the cyclical nature of the pressures to which these materials are exposed exacerbates the problem, requiring the use of materials or a design that not only exhibits sufficient strength but also possesses sufficient fatigue capacity. Over time, the magnitude of the tensile stresses and/or the multitude of cyclical applications of pressurized fluid may result in failure of the pump.
One technique manufacturers have used to combat the tensile stresses applied by the high pressure fluid is to impart residual compressive stresses to the material of the pump exposed to the high pressure fluid. Different manufacturing techniques, such as bead blasting, shot peening, and carburizing may be used to impart such residual compressive stresses or preload. Although the use of compressive residual stresses helps to counter the high tensile stresses to which a material may be exposed, the magnitudes of such residual compressive stresses are limited and are becoming insufficient to counter the continuously increasing tensile stresses that result from the higher injection pressures of today's and tomorrow's fuel systems. Moreover, depending on the location of the material to which one desires to apply a residual preload, the use of one or more of the conventional manufacturing techniques relied upon to impart a residual compressive stress or preload may be difficult. For example, when an area that is exposed to high pressure fluid is located deep within a small bore in a component, it may be difficult to utilize a shot peening or bead blasting technique to impart a compressive preload.
It would be desirable to provide a system and method for applying a compressive preload that is able to overcome one or more of the shortcomings described above.